Control system for synchronizing movement of driven machine members

ABSTRACT

A control system for synchronizing movement of two hydraulically actuated, individually driven and leveled machine members. Preferably, the control unit is used with a pair of hydraulically operated press brakes or other like machines having reciprocable rams which are advanced and retracted by hydraulic fluid under pressure. The control system includes means for detecting the presence and amount of relative motion, and hence lead and lag, between the machine members, means for generating a signal having a polarity indicative of the direction of such relative motion and an amplitude characteristic of the amount of such relative motion, and a valve system having means for decreasing fluid flow into the pressure side of the machine having the leading driven member. The valve is of a proportional flow type in which flow volume is controlled in response to the amplitude of the signal, and, the polarity of the signal determines the machine in which flow of hydraulic fluid will be regulated. In the described form, an electric torque motor is used to control the spool of a three-port hydraulic servo valve having one inlet line from the pressure side of each of the press brakes, a center outlet and a spool land which, in the neutral position thereof, just loses both parts but which will open one or the other upon spool movement in either direction. The torque motor is controlled by an associated amplifier receiving a signal from the signal generator, which is in a form analagous to that of a linear variable differential transformer arranged for rotary movement. The signal generator includes a field disposed in a stationary housing and having a rotary armature, with the drum which serves as a portion of the detector being affixed to a portion of the armature shaft and disposed adjacent the ram on the adjacent press brake, with a flexible but non-extensible drive unit wound over a portion of the drum and being held in tension between a pair of mounting points disposed on either side of the drum. The individual level control system in each press brake is not affected by the synchronizing system.

ijit Gott atet l 1 1 Sept. 11, 1973 CONTROL SYSTEM FOR SYNCHRONIIZING MOVEMENT OF DRIVEN MACHINE MEMBERS [75] Inventor: John R. G011, Oak Forest, 111.

[73] Assignee: Dreis & Krump Manufacturing Company, Chicago, 111;

[22] Filed: Dec. 15, 1971 [21] Appl. No.: 208,380

Primary Examiner-Edgar W. Geoghegan Attorney-Lockwood, Dewey, Zukert & Alex 5 7] ABSTRACT A control system for synchronizing movement of two hydraulically actuated, individually driven and leveled machine members. Preferably, the control unit is used with a pair of hydraulically operated press brakes or other like machines having reciprocable rams which are advanced and retracted by hydraulic fluid under pressure. The control system includes means for detecting the presence and amount of relative motion, and hence lead and lag, between the machine members, means for generating a signal having a polarity indicative of the direction of such relative motion and an amplitude characteristic of the amount of such relative motion, and a valve system having means for decreasing fluid flow into the pressure side of the machine having the leading driven member. The valve is of a proportional flow type in which flow volume is controlled in response to the amplitude of the signal, and, the polarity of the signal determines the machine in which flow of hydraulic fluid will be regulated.

1n the described form, an electric torque motor is used to control the spool of a three-port hydraulic servo valve having one inlet line from the pressure side of each of the press brakes, a center outlet and a spool land which, in the neutral position thereof, just loses both parts but which will open one or the other upon spool movement in either direction. The torque motor is controlled by an associated amplifier receiving a signal from the signal generator, which is in a form analagous to that of a linear variable differential transformer arranged for rotary movement. The signal generator includes a field disposed in a stationary housing and having a rotary armature, with the drum which serves as a portion of the detector being affixed to a portion of the armature shaft and disposed adjacent the ram on the adjacent press brake, with a flexible but non-extensible drive unit wound over a portion of the drum and being held in tension between a pair of mounting points disposed on either side of the drum. The individual level control system in each press brake is not affected by the synchronizing system.

10 Claims, 8 Drawing Figures PAIENTEB SEP] 1 I975 SHEEI 1 BF 3 CONTROL SYSTEM FOR SYNCHRONIZING MOVEMENT OF DRIVEN MACHINE MEMBERS The present invention relates generally to machine controls, and more particularly to a control system for synchronizing the reciprocating movement of. two individually driven and leveled, hydraulically actuated elements. In a preferred form, the invention is incorporated into a control unit for a pair of hydraulically operated press brakes, shears, or other like machines having reciprocable rams, blades or the like which are advanced and retracted by hydraulic fluid under pressure, The invention provides a control system which is adapted to insure that two or more machines may be used in a tandem or aligned relationship with the movement of the ram or the like being synchronized to a very high degree. The invention is also intended to provide a control arrangement whereby a single control may act as a synchronizing control for two or more otherwise separate units operating together, and whereby such a system may at any time be readily and simply disengaged or de-energized to allow either machine to be operated singly, or to permit both machines to be operated at the same time but independently of each other.

In the metal forming art, it is common to employ two or more press brakes or like machines disposed in tandem relation for forming articles which are too long for the forming dies of a single machine. For example, long, thin structural shapes, fencing, light poles, etc., are commonly formed in a pair of tandem hydraulic press brakes. Since most metal forming jobs do not involve parts which are of extreme length in relation to their thickness, and since weight and structural considerations prohibit making press brakes with extremely long rams, ordinary press brakes have a ratio of capacity to length which generally falls within certain ranges. For example, typical hydraulic press brakes of 200 to 300 ton capacities commonly have ram lengths varying between 8 and 16 feet, while larger press brakes of capacities up to 500 or 1,000 tons or more are correspondingly larger, having rams of some 12 to 24 feet or occasionally somewhat more. Such sizes are also common because the work to be formed ordinarily is of a certain length and thickness relationship, that is, thinner sections are usually not excessively long, while thicker sections, such as structural steel parts and the like, often involve bending pieces of greater length. However, when press brakes are to be used in forming parts having great length in relation to their thickness, the tandem arrangement is called for. When satisfactorily carried out, this arrangement permits the majority of day-to-day work to be done on smaller units without sacrificing the ability to perform specialized jobs when the opportunity arises, without making expensive modi' fications or changes to the press brakes, and without sacrificing the ability to operate the machines independently.

In the past, it has been common, to attempt synchronization of two press brakes disposed in tandem by first operating each press brake to determine its average velocity in typical use. This ordinarily determines that one press brake usually operates slightly faster than the other. Thereupon, a synchronizing system is fitted which is adapted to de-energize or bleed fluid from the faster operating press brake from time to time as the ram of the faster brake tends to exceed a predetermined lead over the slower moving or lagging ram of the other press brake. In such a system, the rams move downwardly somewhat together, and if the ram of the faster advancing unit tends to lead, oil is bled therefrom or fed in a reduced quantity thereto until the lagging ram catches up. Upon the return stroke, the rams generally retract at an unequal rate and the cycle is thereafter repeated, with bleeding taking place as the faster ram moves ahead on the downstroke. This system is not fully satisfactory, however, where the speeds of the press brakes happen to coincide very closely, or where speed variation between the machine in use is quite substantial. Likewise, where advancing speed under a rapid advance mode in two speed press brake tends to be faster but the rate of advance is slower in the full tonnage press mode, such a system is unsatisfactory. Moreover, where rate variations occur because of random or indeterminate factors, such a system is inherently unsatisfactory.

Another type of system which has been used is one which bleeds fluid from the pressure side of an advancing ram in response to an undesirably advanced position of the ram, but prior known control systems for such units have involved the use of cross arms, levers, linkages and the like physically connecting the two press brake rams together by either rigid structures or structures having a relatively large number of mechanical parts. In such an arrangement, in addition to lack of accuracy caused by backlash and lack of precision in mechanical movement, such linkages are usually difficult to disassemble and commonly interfere with the use of the press brakes as individual units when they are not being used in tandem.

Other known control systems involve the use of socalled limit switch arrangements wherein, for example, two spaced apart limit switches are placed on one of the rams and a bar placed on the other ram, with a small but certain working clearance separating the working faces of the bar and the limit switches. When the ram containing the bar moves in advance of or behind its intended position of synchronization relative to the other, one or the other limit switch is actuated, thereby decreasing the flow of pressure fluid into the advancing means for the ram or other driven member. The same situation occurs on retraction. A known disadvantage of this type of system is that the bleeding valves usually associated with the limit switches are valves which merely turn on and off, and which accordingly do not respond in proportion to the amount of lead or lag error of one ram in relation to the other. Therefore, if large valves and close working clearances are used, corrective action is rapid, but over-correction and consequent hunting" often occur. If small valves are used, response time is slow; if close clearances are used, the valves are subject to continued operation creating noise and pressure pulsations in the system. Large working clearances decrease sensitivity and accuracy potential. Whereas some of the foregoing problems can be overcome to a certain extent, attempts to do so add cost to the machine and complexity and reduce reliability.

Accordingly, in view of the shortcomings of the foregoing and other prior art synchronizing devices, it is an object of the present invention to provide an improved synchronizing control system for a pair of individually actuated machine members adapted to be operated together.

Another object is to provide an improved control system for use with press brakes or like machine which may be added thereto without substantial increase in cost, and which may be readily de-energized or disconnected to permit each machine to be used individually.

Another object is to provide a system of improved reliability and simplicity and which affords proportional error control and rapid response.

Another object is to provide such an apparatus capable of a high degree of accuracy and repeatability in synchronizing the movement of two relatively movable machine members forming parts of separate but adjacently disposed machines and which may be deenergized or disconnected to permit separate operation of such machines with a minimum of trouble and without affecting the operation of the individual machines.

Another object of the invention is to provide a system which includes means for control of oil transferred through the synchronizing system to insure that each machine maintains an adequate oil supply regardless of synchronizing conditions.

Another object is to provide, in combination, a pair of machines each having individually operated and leveled movable members for performing work on a single workpiece and a novel synchronizing control system adapted to maintain synchronous movement of the members in use.

Another object is to provide a control system in which a single detector determines which of a pair of driven machine members is in advance of a desired position as well as the amount that such member is in advance of the desired position, and which includes means for creating a signal reflecting the condition so that fluid flow may be controlled in the pressure side of the correct machine and whereby the flow may be controlled in relation to the amount of advance present at any given time.

Another object is to provide a synchronizing system in which correction is proportional to the magnitude of this error signal received by a detector associated with one of the movable members.

A further object is to provide an apparatus having means for detecting which of a pair of machine members is in advance of an intended position thereof, means for creating a signal having a predetermined polarity and magnitude so as to identify the advance member and to indicate the degree of advance thereof, means for providing corresponding motion to the means for controlling the flow of pressure fluid to the means for advancing and retracting the member in proportion to the degree. of such advance.

The foregoing and other objects and advantages of the invention are accomplished by providing a control system which includes a detector unit and a signal generator, with the detector being adapted to provide an indication of which of a pair of relatively movable members is in advance of its intended position and the degree of such advance, and an operative connection to a fluid control system adapted to reduce the amount of pressure fluid furnished to the drive system for the member which is in advance of its intended position, preferably reducing fluid flow in proportion to the degree of advance. The manner in which these and other objects and advantages of the invention, including those inherent therein, are accomplished will become more apparent when reference is made to the following detailed description of a preferred embodiment of the invention set forth by way of example and shown in the accompanying drawings, wherein like reference numbers indicate corresponding parts throughout.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing a pair of hydraulic press brakes arranged in tandem with each other and adapted to have the rams thereof move simultaneously for forming an elongated workpiece;

FIG. 2 is a diagrammatic view showing the rear end portions of a pair of press brakes made according to the invention disposed with end portions thereof closely adjacent each other and showing the provision of an individual leveling system for each ram and the provision of the novel control system to synchronize the movement of one ram in respect to movement of the other ram;

FIG. 3 is a greatly enlarged fragmentary view of the movement detector and signal generator assembly of the present invention;

FIG. 4 is a top plan view of the movement detector and signal generator assembly of FIG. 3;

FIG. 5 is a vertical sectional view of the movement detector and signal generator assembly of FIGS. 3 and 4 taken along lines 5-5 of FIG. 4;

FIG. 6 is a schematic view of the principal parts of the hydraulic circuit of the present invention;

FIG. 7 is a schematic view showing the relation of they hydraulic flow control valve, the torque motor for driving the same, and the detector and signal generator assembly of the invention; and

FIG. 8 is a view of a signal generator and the associated torque motor and flow control valve, showing certain elements both schematically and pictorially.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION Although it will be understood that the principles of the invention are applicable to a number of forms of machines and apparatus, and that the invention might be embodied in a number of different forms and adapted for various uses, a detailed description thereof will be made only in reference to an embodiment wherein the machine members to be driven are the ram portions of a pair of adjacently disposed hydraulically actuated press brakes, wherein oil is the pressure fluid to be used, and is driven by positive displacement pumps actuated by electric motors, wherein the control of oil flow within each of the individual press brakes is carried out by a three-position hydraulic servo valve, wherein the servo valve is actuated electrically by a torque motor, wherein a tape and drum system is used to sense differential movement of two members, and wherein the signal generator providing an output indicative of polarity and magnitude of differential movement is operatively associated with the detecting means.

Referring now to the drawings in greater detail, FIG. I shows the invention to be preferably adapted for use in synchronizing the operation of a pair of similar or identical press brakes 20, 22, and each including a generally C-shaped frame unit 24, 26, vertically movable rams 28, 30 and fixed beds 32, 34. The beds 32, 34 support fixed lower tooling 36, 38 which supports the work which is acted upon respectively by upper tools 40, 42. Pairs of hydraulic piston and cylinder assemblies 44, 46 are provided to reciprocate the rams 28, 30 vertically,

moving them down under high force and retracting them for repetition of the power stroke. In forming a single workpiece, it is essential that the movement of rams 28,30 be precisely synchronized so that the opposed pairs of upper and lower tools 40, 36 and 42, 38 will meet in aligned relation and will contact the work simultaneously.

Referring now to FIG. 2, as the press brakes 20, 22 are seen from the rear, it will be noted that each individual ram 28, contains a level control system generally designated 50, 52, and that each leveling system includes a pair of rollers 54 and a flexible steel tape or cable 56 anchored at a fixed point 58 on the bed or frame and having the other end 60 thereof received within a level control cabinet 62. This system of leveling each individual ram 28, 30 is well known in the art, and generally comprises a directly actuated hydraulic bleed valve within the cabinet or housing 62, limit switches to operate bleeding valves, or, in certain constructions, electric signalling means to reduce the output of either of the pumps serving the hydraulic cylinders which move the rams. Accordingly, if the ram remains level, up and down movement of the ram will not cause up or down'movement of the end 60 of the tape 56, and the ram will remain level. If the ram tilts counter-clockwise as shown in FIG. 2, the end 60 of the tape 56 may move upwardly under the influence of a spring or the like within the cabinet 62. This causes actuation of the servo valve, bleeding limit switches or pump control switches associated with one cylinder. Tilting the ram clockwise as shown in FIG. 2 will in effect move the end 68 of the tape downwardly, causing fluid to be bled from the other cylinder, or the fluid input thereto to be reduced or throttled. Inasmuch as the foregoing leveling systems are conventional in the art, further description thereof is not considered necessary to an understanding of the present invention. Such systems are illustrated, however, in the Castle U.S. Pat. No. 2,558,071, the Hazelton et al. U.S. Pat. No. 2,978,976, and the Munschauer et al. U.S. Pat. No. 3,059,431. Accordingly, it will be understood that each of the individual press brakes 28, 30 is intended to be equipped in a conventional manner with its own leveling system, since the present invention does not in any way deal with or affectin use the operation of the leveling system.

Referring again to FIG. 2, it will be noted that the control system of the present invention includes a novel combination movement detector and signal generator system generally designated 64 which is operatively associated, as by electrical connections 66, to a fluid flow control system generally designated 68. The detector and signal generator system 64 is shown in detail in FIGS. 3, 4, 5 and 8, while the flow control system generally designated 68 is shown in detail in FIG. 6.

Referring now to FIGS. 3-5, it will be seen that the detector and signal generator 64 includes a movement detector portion generally designated 70 and asignal generator portion is designated 72. The signal generator includes an exterior housing 74 which includes therein an electrical field 76 shown diagrammatically in broken lines. Disposed within the field 76 is a rotatable armature portion 78, also shown in broken lines. The signal generator housing 74 is fixedly mounted on a plate 80 which is held against sideways movement but mounted to permit vertical adjustment within a pair of side guides 82. Also fixedly mounted to the plate 80 is a drum support bracket 84 extending outwardly from the housing 74 and parallel to the axis thereof. The bracket 84 includes a flange 86 at the end thereof for journaling one end portion 88 of a shaft 90 with an en-v larged diameter drum 92 mounted thereon. The rotatable armature 78 is affixed to the shaft 90 so that any rotation of the drum 92 will result in an exactly corresponding rotation of the armature 78.

As is best shown in FIGS. 4 and 5, the bracket 84 is fixedly secured to the plate 80 and hence to the ram 28, but is entirely free of physical contact with the ram 30, except for the driving connection afforded by the drive means in the form of a tape 94. The tape 94 serves as a means for rotating the drum 92 when relative movement of the rams 28, 30 occurs, since the tape 94 is secured at the upper end thereof to the top portion 96 of the ram 30 by a fastener 98, and is also fastened by a fastening assembly 100 to the bottom portion of the ram 30. The fasteners 98, 100 are laterally offset from each other so that the tape 94 may be trained around the drum a plurality of times without being wound upon itself.

The spring 102 forming a connection to the ram 30 is relatively strong and permits the tape 94 to be placed in tension; however, as will be pointed out, the lower end portion of the tape 94 does not ordinarily move in use. As shown in FIGS. 4 and 5, the tape may be fastened by means such as a clamp 104 to the drum 92. As shown, two separate tape halves are used with each having an end fixed to the drum; the effect is that of a single tape trained over the drum, however.

Referring again to FIG. 3, it will be noted that means for adjustably positioning the signal generator and detector unit 64 are provided in the form of a rotatable knob 106 having a shank portion 108 with screw threads thereon extending through a threaded mounting bracket 110 and terminating in a bracket 112 forming a part of the plate 80. Accordingly, for making an initial adjustment, the knob 106 may be rotated to position the signal generator housing 74 in any desired vertical position. The flexible connector permits such adjustment to be made without damaging the electrical connections 66.

Referring now to FIGS. 6 and 8, the fluid flow control portion of the system is illustrated. FIG. 6 schematically shows the system 68 to include a pressure line 1 14 from the left-hand press brake, a pressure line 1 16 from the right-hand press brake, and a line 118 which serves as a source of pilot pressure, and which includes an oil filter 119. The operational mode selector valve 120 is shown to be operated by a solenoid 122, which, when energized by current furnished through an electrical connection 124, opens the appropriate port to pilot hydraulic pressure from line 132, thereby filling a chamber 134 and pushing the spool 126 of the valve 120 to the left as shown in FIG. 6. This permits pressure fluid in lines 1114, 116 to be supplied to lines 128, 130. Although only one chamber 134 is shown, it is understood that two chambers may be provided or that the spool 126 may be spring returned. When the solenoid 122 closes the port from line 132 to the chamber 134, pilot fluid therein drains to a sump through line 136 in a conventional manner.

Although lines 128, are filled prior tooperation of the synchronizing system, the flow of pressure fluid into the bleed or relief line 138 is normally prevented since the spool 140 of the synchronizing control valve 142 is exactly centered. As schematically shown in FIG. 6, if the spool is moved to the right, communication will be established between pressure line 130 and the drain line 138, whereas movement of the spool 140 to the left will create communication between pressure line 128 and drain line 138. Accordingly, if the spool 140 is moved to the right, fluid will be bled from the right-hand press brake served by line 116, and if the spool is moved to the left fluid will be bled from the left-hand press brake served by line 114.

Although the symbol used to show the valve 142 is a conventional .loint Industry Conference symbol, it must be understood that this valve 142 is of a type having two normally open inlet ports and a spool 140 which just closes a single center exhaust port. Therefore, the space on either side of the center land 144 is filled with pressure fluid. Thus, as can be seen in FIG. 8, the land 144 just blocks the opening 146 in the bottom of the valve, preventing fluid flow out the drain port 146. However, the arrows 148, 150 indicate that fluid pressure is being supplied to the interior of the valve 142 through two different sources, it being understood that ports 148, 150 are connected to pressure lines 128, 130. In the preferred form, the overlap between the land 144 of the spool 140 and the port 146 is merely enough to prevent fluid leakage, preferably 0.001 inches or less.

At the bottom of FIG. 6, a third valve generally designated 152 is shown to include a solenoid 154, a pilot chamber 156 and a center spool 158. In the position shown in FIG. 6, the spool 158 establishes communication between line 138, from which all synchronizing oil is drained to a line 160 ending in a sump 162 which will be assumed to be associated with the slave or following press brake. Line 164 communicates with the sump 166 in the master press brake, and accordingly, movement of the spool 158 to the right will establish communication between the line 138 and the tank of the master machine. A pilot line 168 also serves to perform the physical movement of the valve spool 168 in response to an electrical signal fed to the solenoid 154 through electrical connection 170. After each movement of the valve spool, pilot oil is bled through line 172 to an appropriate sump.

Referring now to the operation of the control system of the invention, it will be assumed that the two machines are positioned adjacent each other with all connections made as shown in FIGS. 26. Upon actuation of an operating switch, the spool 126 of the valve 120 is shifted to the position shown in FIG. 6, which permits pressure oil from both of the press brakes 20, 22 to enter the lines 114, 116, and to pass through the valves 120 into lines 128, 130. Referring to FIG. 2, it will be noted that the line 114 is associated with the left-hand press brake and the line 116 with the right-hand press brake 22; the lines 116 are preferably attached to the hydraulic pressure system of the press brake at a point in the line connecting the upper portions of the cylinders to .the safety valve, and accordingly the flow of fluid in line 114 or 116 will not take the fluid exclusively from one cylinder or the other, and thus will not adversely affect the leveling. With the system arranged as just described, the operating switch may be actuated and the press brake rams 28, 30 will move up and down in a conventional manner, except that the depth stop or bottom limit switch and the top limit switch are customarily de-energized on one machine and the signal to reverse ram direction is therefore generated from a single source only. As long as the rams 28, 30 remain in exactly synchronized relation, no relative movement of the bracket 84 and its associated parts with respect to the ram 30 will occur, and no signals will be generated. However, assuming for example that the left-hand ram 28 begins to lead or take up a position in advance of its intended position on the downstroke, the bracket 84 must be moved downward with respect to the ram 30. In so doing, the drum must be rotated to permit this movement without imposing a bending moment on the bracket 84. The tape 94 is not affected in length, however, since any downward movement of the drum 92 taking up tape will be exactly compensated for by paying out tape above the drum 92. Thus, the drum merely revolves a linear distance equal to the amount of lead or lag error. As a result, referring to FIG. 8, where the field 76 is shown as a pair of coils, and where the armature 78 is shown in solid lines and mounted for rotation, the armature will move toward one or the other of the dotted line positions shown, depending upon the direction of drum rotation. As a result, a characteristic signal will be generated in the coils in the field 76, and this signal will, when suitably increased by an amplifier (not shown), appear in the coils 174 of a torque motor generally identified as 176. Rotational force applied to the torque motor will cause the torque am 178 to be moved from the solid line position thereof toward one or the other of the dotted line positions, depending both upon the direction in which the armature 78 was moved and upon the distance that the armature moved.

Thus, a clockwise movement of the armature 78 might cause a counter-clockwise movement of the arm 178, thereby causing the rod 180 to move to the right, moving the entire spool to the right and opening communication between the pressure port 148 and the exhaust port 146, and vice versa. Since spool displacement is proportional to the strength of the applied signal, ram response is proportional to lead error. The right-hand side of FIG. 8 shows diagrammatically the arrangement of the valve 142 pictorially shown on the left-hand side thereof.

Inasmuch as both press brakes are adapted to be moved under pressure to the downward position as well as to the upward position, it is possible for a given ram to be ahead of its intended position on the upstroke as well as the downstroke. However, if excess fluid is being pumped in the left-hand press brake 20, the ram 28 will tend to be in a lower position on the downstroke, thereby lowering the drum 92 in respect to the position shown. Arbitrarily assuming this lowered drum position to create a positive polarity signal, a raised position of the drum 94 will create a negative polarity signal. On the upstroke, however, if excess fluid continues to be pumped in the left-hand press brake 20, the ram 28 will tend to lead, except that a lead will be manifested by a relative raising of the ram 28 causing an opposite or clockwise rotation of the drum 92. Were this rotation to indicate a negative polarity signal, fluid flow might be reduced in the right-hand or trailing press brake, aggravating the out-of-synchronous condition instead of correcting it. Accordingly, as shown schematically in FIG. 8 by the alternate plus and minus signals, the electrical connections are reversed each time the direction of ram travel is reversed, thereby insuring that correction always occurs in the intended direction regardless of the direction of ram movement.

As is well known to those skilled in the art, a similar effect might be achieved by hydraulic means by crossing the connections in lines 128 and 130 or lines 114 and 116 each time the machine direction is reversed.

Referring now to FIG. 7, and to the lower portion of FIG. 6, the preferred form of machine is made so that one tank 162 is associated with the slave machine, and accordingly all fluid which is bled through line 138 is furnished to line 160 and to the sump 162 under'ordinary conditions. Eventually, however, the tank associated with line 160 becomes full, and the float 182 operates a switch 184, producing a detectable signal in the electric line 170 which is fed to the solenoid 154 of the valve 152. This moves the spool 158 of the valve 152 to the opposite position, shown in FIG. 6, causing fluid to be passed through line 164 into the sump 166 of the other press brake, until the float 182 returns to a lower position, thereby extinguishing the signal in line 170 and causing the directional valve 152 to revert to its initial orientation.

Accordingly, meansv are provided for insuring that one oil supply tank or the other of the press brakes will not be undesirably over filled, as would be a problem if considerable volumes of oil were bled to line 138 from time to time. 7

As shown in FIG. 8, there is a direct mechanical connection 180 between the arm 178 of the torque motor 176 and the spool 140 of the valve 142; and an electrical connection 66 between the windings 174 of the torque motor and the field 76 of the signal generator. in FIG. 2, the components also shown in FIG. 8 are diagrammatically illustrated, it may be seen that the line 66 furnishes a signal to the torque motor 176, causing movement of the rod 180 to move the spool of the servo valve 142, thereby bleeding fluid through line 138 and to the selector valve 152 to which are connected lines 160, 164 and which terminate respectively at the oil supply tanks of either machine.

The foregoing detailed description has shown certain preferred means for performing the operations indicated. However it is apparent that a number of different arrangements and substitutions might be made in a construction which would followthe principles of the invention but which would be embodied in different forms. For example, the tape 94 might be replaced by a Bowden wire or cable, associated with a grooved drum or the like. Likewise, the drum 92 might be replaced by a rotary pinion gear, and driving contact to ram 30 might be made by a rack associated therewith. The mounting of the housing 74 of the signal generator 72 might be made in other ways, for example, the unit could be fixed and adjustment could be provided by means of an adjustment in the shaft 90. The principles of the invention might also be carried out by using a relative movement detector of either of the types described above or their equivalent, and in place of the signal generator 72 and the torque motor 176, utilizing a direct connection to'the spool 140 of the servo valve 142, the effect of reversing of electrical polarity with directional change might be accomplished hydraulically, as referred to above. Other variations may readily occur to those skilled in the art.

it will thus be seen that the present invention provides a novel synchronization control having a number of advantages and characteristics including those pointed out herein and others which are inherent in the invention. It will also be understood that a'number of variations and modifications to the described form of apparatus may occur to those skilled in the art and it is anticipated that such changes and modifications may be made without departing from the spirit of the invention or the scope of the appended claims.

We claim:

1. A synchronizing system for synchronizing the movement of two individually leveled and hydraulically driven machine members, said system including variable capacity means associated with each hydraulically driven member for controlling the flow of driving fluid thereto in response to an applied control signal to reduce the speed of movement thereof, means for detecting which of said members is in advance of its intended position relative to the other of said members and for detecting the amount of such advance, means for generating a control signal of a polarity indicating which member is advanced and of a magnitude proportional to the amount of such advance, and means for applying said control signal to said variable capacity means whereby relative movement of one member to the other causes a speed reduction of the member which is in advance of the other member in proportion to the amount of such advance at any time.

2. A synchronizing system as in claim 1 in which said variable capacity means comprise an electro-hydraulic servo valve having a flow rate therethrough which is in direct proportion to the magnitude of said control signal.

3. A synchronizing system for synchronizing the movement of two individually leveled and hydraulically driven machine members, said system including variable capacity means associated with each hydraulically driven member for reducing the flow of driving fluid thereto in order to reduce the speed of movement thereof, means for detecting which of said members is in advance of its intended position relative to the other of said members and for detecting the amount of such advance, means comprising a transformer for generating a signal of a polarity indicating which member is advanced and of a magnitude proportional to the amount of such advance, and an operative connection including an amplifier for said signal between said signal generating means and said means for controlling fluid flow, whereby relative movement of one member to the other generates a signal causing a speed reduction of the member which is in advance of the other member in proportion to the amount of such advance at any time.

4. A synchronizing system for synchronizing the movement of two individually leveled and hydraulically driven machine members, said system including: variable capacity means associated with each hydraulically driven member for reducing the flow of driving fluid thereto in order to reduce the speed of movement thereof; means, including an elongated flexible but non-extensive drive unit having both ends thereof fixed to one of said machine members, and a rotatable drum fixedly positioned with respect to the other of said machine members, said drive unit being trained over said rotatable drum whereby relative movement of said members creates drum rotation in a characteristic direction, for detecting which of said members is in advance of its intended position relative to the other of said members and for detecting the amount of such advance; means for generating a signal of a polarity indicating which member is advanced and of a magnitude proportional to the amount of such advance; and an operative connection between said signal generating means and said means for controlling fluid, flow, whereby relative movement of one member to the other generates a signal causing a speed reduction of the member which is in advance of the other member in proportion to the amount of such advance at any time.

5. A synchronizing system for synchronizing the movement of two individually leveled and hydraulically driven machine members, said system including variable capacity means associated with each hydraulically driven member for reducing the flow of driving fluid thereto in order to reduce the speed of movement thereof, means for detecting which of said members is in advance of its intended position relative to the other of said members and for detecting the amount of such advance, means for generating a signal of a polarity indicating which member is advanced and ofa magnitude proportional to the amount of such advance, and an operative connection between said signal generating means and said means for controlling fluid flow, whereby relative movement of one member to the other generates a signal causing a speed reduction of the member which is in advance of the other member in proportion to the amount of such advance at any time, and means for returning pressure fluid to one or the other of the fluid systems in response to a control signal from one of the systems, said control signal responding to the pressure fluid level in one of said systems.

6. A control system for synchronizing the movement of two hydraulically driven machine members each driven by a separate source of fluid under pressure, said system including means for detecting which of a pair of relatively movable members is in advance of its intended position relative to the other member and for indicating the degree to which said member is in advance of said other member, means for reducing the amount of pressure fluid furnished to the drive system of each member in proportion to the strength of a received control signal, means for generating a control signal having a characteristic polarity and magnitude indicative of which member is in advance of its intended position and the degree thereof, and an operative connection between said detecting means and said signal generating means and an operative connection between said signal generating means and said means for reducing fluid flow.

7. 'A system for leveling a pair of press brakes having one end portion of one of the rams thereof disposed adjacent another end of the ram of the other press brake, said system including means creating an electromagnetic field affixed to one of said rams, an armature rotatable within said field, a drum operatively attached to said armature, said drum and armature being fixed against translatory movement with respect to said one ram, an elongated flexible but non-extensible drive means having the center portion thereof trained over said drum in driving relation and both end portions fixed to spaced apart portions of said other ram, said armature and field producing a signal of characteristic polarity and intensity dependent on the degree and direction of drum rotation, a pressure fluid line extending from each press brake to a single valve with a spool adapted to move in either direction from a centered position to bleed fluid from the fluid system of one or the other of said press brakes, and means for actuating said single valve in response to said signal, said valve spool moving in a direction indicated by the polarity of said signal, whereby differential ram movement causes actuation of said valve and acts to retard the movement of the advanced ram.

8. A system as defined in claim 7 wherein said flexible but non-extensible drive means is in the form of a flat, flexible steel tape.

9. A system as defined in claim 7 wherein said field and armature comprise a differential transformer.

10. A system as defined in claim 7 in which flow through said valve is in direct proportion to the displacement of said spool, whereby ram speed correction is proportional to differential movement of said rams. #k 

1. A synchronizing system for synchronizing the movement of two individually leveled and hydraulically driven machine members, said system including variable capacity means associated with each hydraulically driven member for controlling the flow of driving fluid thereto in response to an applied control signal to reduce the speed of movement thereof, means for detecting which of said members is in advance of its intended position relative to the other of said members and for detecting the amount of such advance, means for generating a control signal of a polarity indicating which member is advanced and of a magnitude proportional to the amount of such advance, and means for applying said control signal to said variable capacity means whereby relative movement of one member to the other causes a speed reduction of the member which is in advance of the other member in proportion to the amount of such advance at any time.
 2. A synchronizing system as in claim 1 in which said variable capacity means comprise an electro-hydraulic servo valve having a flow rate therethrough which is in direct proportion to the magnitude of said control signal.
 3. A synchronizing system for synchronizing the movement of two individually leveled and hydraulically driven machine members, said system including variable capacity means associated with each hydraulically driven member for reducing the flow of driving fluid thereto in order to reduce the speed of movement thereof, means for detecting which of said members is in advance of its intended position relative to the other of said members and for detecting the amount of such advance, means comPrising a transformer for generating a signal of a polarity indicating which member is advanced and of a magnitude proportional to the amount of such advance, and an operative connection including an amplifier for said signal between said signal generating means and said means for controlling fluid flow, whereby relative movement of one member to the other generates a signal causing a speed reduction of the member which is in advance of the other member in proportion to the amount of such advance at any time.
 4. A synchronizing system for synchronizing the movement of two individually leveled and hydraulically driven machine members, said system including: variable capacity means associated with each hydraulically driven member for reducing the flow of driving fluid thereto in order to reduce the speed of movement thereof; means, including an elongated flexible but non-extensive drive unit having both ends thereof fixed to one of said machine members, and a rotatable drum fixedly positioned with respect to the other of said machine members, said drive unit being trained over said rotatable drum whereby relative movement of said members creates drum rotation in a characteristic direction, for detecting which of said members is in advance of its intended position relative to the other of said members and for detecting the amount of such advance; means for generating a signal of a polarity indicating which member is advanced and of a magnitude proportional to the amount of such advance; and an operative connection between said signal generating means and said means for controlling fluid flow, whereby relative movement of one member to the other generates a signal causing a speed reduction of the member which is in advance of the other member in proportion to the amount of such advance at any time.
 5. A synchronizing system for synchronizing the movement of two individually leveled and hydraulically driven machine members, said system including variable capacity means associated with each hydraulically driven member for reducing the flow of driving fluid thereto in order to reduce the speed of movement thereof, means for detecting which of said members is in advance of its intended position relative to the other of said members and for detecting the amount of such advance, means for generating a signal of a polarity indicating which member is advanced and of a magnitude proportional to the amount of such advance, and an operative connection between said signal generating means and said means for controlling fluid flow, whereby relative movement of one member to the other generates a signal causing a speed reduction of the member which is in advance of the other member in proportion to the amount of such advance at any time, and means for returning pressure fluid to one or the other of the fluid systems in response to a control signal from one of the systems, said control signal responding to the pressure fluid level in one of said systems.
 6. A control system for synchronizing the movement of two hydraulically driven machine members each driven by a separate source of fluid under pressure, said system including means for detecting which of a pair of relatively movable members is in advance of its intended position relative to the other member and for indicating the degree to which said member is in advance of said other member, means for reducing the amount of pressure fluid furnished to the drive system of each member in proportion to the strength of a received control signal, means for generating a control signal having a characteristic polarity and magnitude indicative of which member is in advance of its intended position and the degree thereof, and an operative connection between said detecting means and said signal generating means and an operative connection between said signal generating means and said means for reducing fluid flow.
 7. A system for leveling a pair of press brakes having one end portion of one of the rams thereof disposed adjacent another end Of the ram of the other press brake, said system including means creating an electromagnetic field affixed to one of said rams, an armature rotatable within said field, a drum operatively attached to said armature, said drum and armature being fixed against translatory movement with respect to said one ram, an elongated flexible but non-extensible drive means having the center portion thereof trained over said drum in driving relation and both end portions fixed to spaced apart portions of said other ram, said armature and field producing a signal of characteristic polarity and intensity dependent on the degree and direction of drum rotation, a pressure fluid line extending from each press brake to a single valve with a spool adapted to move in either direction from a centered position to bleed fluid from the fluid system of one or the other of said press brakes, and means for actuating said single valve in response to said signal, said valve spool moving in a direction indicated by the polarity of said signal, whereby differential ram movement causes actuation of said valve and acts to retard the movement of the advanced ram.
 8. A system as defined in claim 7 wherein said flexible but non-extensible drive means is in the form of a flat, flexible steel tape.
 9. A system as defined in claim 7 wherein said field and armature comprise a differential transformer.
 10. A system as defined in claim 7 in which flow through said valve is in direct proportion to the displacement of said spool, whereby ram speed correction is proportional to differential movement of said rams. 